The world's native languages are dying out at an unprecedented (空前的) rate, taking with them irreplaceable knowledge about the natural world, according to a new study.

　　The study identified five global "hot spots" where languages are vanishing faster than anywhere else -- eastern Siberia, northern Australia, central South America, the US state of Oklahoma and the US Pacific Northwest. "Languages are suffering a global extinction crisis that greatly goes beyond the pace of species extinction," linguistics (语言学的) professor David Harrison noted, who said half of the world's 7, 000 languages were expected to disappear before the end of the century.

　　Native people had an intimate (详尽的) knowledge of their environment that was lost when their language disappeared, along with other certain things often unfamiliar to us, Harrison stressed. "Most of what we know about species and ecosystems is not written down anywhere, it's only in people's heads," he said. "We are seeing in front of our eyes the loss of the human knowledge base."

　　Harrison was one of a team of linguists who carried out the study. The researchers travelled to Australia this year to study native languages, some of the most endangered. According to Harrison, in Australia, they were heartened to see a woman in her 80s who was one of the only three remaining speakers of the Yawuru language passing on her knowledge to schoolchildren. He said such inter-generational exchanges were the only way native languages could survive. "The children had elected to take this course, no one forced them," he said. "When we asked them why they were learning it, they said, 'This is a dying language, we need to learn it'." Also, while there they found a man with knowledge of the Amurdag language, which had previously been thought extinct.

　　The researchers said all five of the hot spots identified were areas that had been successfully colonized (殖民) and where a dominant language such as Spanish or English was threatening native tongues.

　　21. The underlined word "vanishing" in the second paragraph can be best replaced by ______.

　　A. developing B. changing C. increasing D. disappearing

　　22. According to Harrison, language extinction ______.

　　A. causes the researchers lots of worries

　　B. speeds up the pace of species extinction

　　C. threatens the existing of Spanish and English

　　D. brings about a loss of knowledge about the environment

　　23. Which of the following can be described as good news?

　　A. Native languages became less endangered in Australia.

　　B. A man was found with knowledge of the Amurdag language.

　　C. Researchers were well received by native people in Australia.

　　D. Many schoolchildren showed interest in the Yawuru language.

　　24. According to the text, native languages were endangered partly because of ______.

　　A. few researches done on them

　　B. the small population of native people

　　C. the strong influence of ruling languages

　　D. little education native people receive at school

　　Very mobile ears help many animals direct their attention to the rustle of a possible attacker. Researchers say these mobile ears have become a useful communication tool. Their studies of animal behaviour build up a picture of how communication and social skills developed.

"We're interested in how they communicate," said lead researcher Jennifer Wathan. "And being sensitive to what another individual is thinking is a fundamental skill from which other more complex skills develop."